Disc drives are data storage devices that store digital data in magnetic form on a rotating disc. Modern disc drives comprise one or more rigid information storage discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (“heads”) mounted to a radial actuator for movement of the heads relative to the discs. During a write operation sequential data is written onto the disc track, and during a read operation the head senses the data previously written onto the disc track and transfers the information to an external environment. Important to both of these operations is the accurate and efficient positioning of the head relative to the center of the desired track on the disc. Head positioning within a desired track is dependent on head-positioning servo patterns, i.e., a pattern of data bits recorded on the disc surface and used to maintain optimum track spacing and sector timing. Servo patterns or information can be located between the data sectors on each track of a disc (“embedded servo”), or on only one surface of one of the discs within the disc drive (“dedicated servo”). Regardless of whether a manufacturer uses “embedded” or “dedicated” servos, the servo patterns are typically recorded on a target disc during the manufacturing process of the disc drive.
Recent efforts within the disc drive industry have focused on developing cost-effective disc drives capable of storing more data onto existing or smaller-sized discs. One potential way of increasing data storage on a disc surface is to increase the recording density of the magnetizable medium by increasing the track density (i.e., the number of tracks per millimeter). Increased track density requires more closely-spaced, narrow tracks and therefore enhanced accuracy in the recording of servo-patterns onto the target disc surface. This increased accuracy requires that servo-track recording be accomplished within the increased tolerances, while remaining cost effective.
Servo patterns are typically recorded on the magnetizable medium of a target disc by a servo-track writer (“STW”) assembly during the manufacture of the disc drive. One conventional STW assembly records servo pattern on the discs following assembly of the disc drive. In this embodiment, the STW assembly attaches directly to a disc drive having a disc pack where the mounted discs on the disc pack have not been pre-recorded with servo pattern. The STW essentially uses the drive's own read/write heads to record the requisite servo pattern directly to the mounted discs. An alternative method for servo pattern recording utilizes a separate apparatus having dedicated servo recording transducers or heads for recording servo pattern onto one or more discs. The dedicated servo recording heads can be used to record servo information to a number of discs simultaneously, which are subsequently loaded into the disc drive for use. In light of the trend toward higher track density, there is a demand for dedicated STW assemblies that are capable of recording servo patterns simultaneously to multiple discs for high density disc drives.
Conventional dedicated STW assemblies are oriented in a horizontal direction with the discs mounted in a horizontal plane. Such dedicated STW assemblies typically utilize one or more actuator arms having one or more transducers or heads on each arm which, in turn, move in a horizontal plane along a radius of the magnetizable medium on the target disc. That is, conventional dedicated STWs have both discs and actuator arms that rotate in a horizontal plane about a vertical STW bearing axis so that a head at a distal end of each actuator arm moves in a horizontal path across the disc surface.
Shortcomings of the prior art horizontally-oriented STW assemblies include disc alignment errors and imperfections in the recording system resulting from the horizontal orientation of both the discs and the actuator arms, as well as the flexible “suspensions” connecting the servo-writing heads to the actuator arms. Specifically, while the discs are formed from a relatively stiff metal material, the discs are nonetheless subject to gravity-induced warping, particularly along the outer circumference of the discs. Even miniscule amounts of gravity-induced disc warpage can lead to unacceptable servo-writing errors, particularly in light of the higher track densities demanded by current disc drive users.
Accordingly, improvements in servo pattern recording accuracy are required by dedicated STW assemblies as well as improvements in the time it takes to manufacture discs having the appropriate servo pattern. The present invention provides a solution to this and other problems, and offers other advantages over the prior art.